Updated Delta+BOHE Impl in Java

[James M Snell <[e-mail]>]

I have updated my experimental Delta+Bohe java implementation to match
the current draft of the specification and Roberto's current delta
iteration. I still have to patch this in to the compression-test stuff
but the code is functional.

  https://github.com/jasnell/http2

Requires maven to build. Dependencies are light. Still needs a ton of
work and I have not even started working on performance optimizations.
It's a pretty straight forward port of everything Roberto has done in
the python impl.

The one bit this does add is multi-type header values. The types
supported are String, Number, Datetime and Binary. Strings can be
either UTF-8 or ISO-8859-1. If they are ISO-8859-1, they can be
Huffman coded using Roberto's static code. I am using an different
static dictionary of predefined header values tho.

General takeaways ..

1. The implementation is not that difficult to do and seems to perform
reasonably well.
2. The additional types are very useful and add minimal additional
complexity to the implementation.
3. I'm generally not convinced that we really need the huffman coding.
Yes, it saves a handful of bytes here and there but it does add
additional complexity. I can live with it tho. If we keep it and we
decide to allow for UTF8 header values, then we need to come up with a
static huffman coding that includes the extended UTF8 character
support.
4. Performance seems reasonable overall.

I'm going to be working on implementing HeaderDiff next. Hopefully
I'll have the time to have that done by this Friday.

- James